1. Field of the Invention
This invention relates to a tuning apparatus for a laser and, more particularly, to an assembly for a birefringent filter tuner.
2. Description of the Prior Art
Many types of lasers can be tuned over a small wavelength range; however, only a few types are tunable over a broad enough range to be considered truly "tunable." The most common type of tunable laser is the dye laser, in which the laser medium is a solution of an organic dye. In recent years, several tunable solid state lasers have been disclosed; most notably, the alexandrite laser (U.S. Pat. No. 4,272,733).
Tuning of tunable lasers may be accomplished in several different ways. In general, tuning is accomplished by including within the optical resonator an optical element with wavelength-selective properties, so that only light having a certain (selectable) wavelength is favored for amplification by the active medium. For example, the optical element may be a prism, a lens having longitudinal chromatic aberration, or an optical grating. A preferred tuner consists of one or more birefringent filters.
The theory, design, and operation of birefringent filter tuners have been described by G. Holtom et al., IEEE, J. Quantum Electron. QE-10, 577 (1974); J. M. Yarborough et al., U.S. Pat. No. 3,868,592, issued Feb. 25, 1975; and D. R. Preuss et al., Appl. Opt. 19, 702 (1980). In practice, one or more birefringent crystal plates are placed in the laser cavity at Brewster's angle to the direction of the laser beam. A single plate acts as a wavelength selector, with tuning accomplished by rotating the plate about an axis normal to its surface. By adding additional plates, the output beam wavelength peak can be narrowed. The thickness of each plate in a tuner is an integral multiple of the thickness of the thinnest plate. The plates are maintained in a parallel array, which is rotated as a unit for tuning. Optimum performance of the tuner requires that the optic axes of all the plates be precisely aligned. Although apparatus for birefringent tuners and methods for orienting their multiple plates have been disclosed in the references cited above, none describes a tuner assembly that permits convenient plate orientation, ensures that the orientation is not disturbed when the plates are clamped into place, and readily permits the clamping operation to be reversed.